Numerical Simulations of Gas Flow Patterns Within a Tall-Form Spray Dryer

Abstract

Numerical simulations of the air flow patterns within a small scale tall-form countercurrent spray dryer have been performed. The simulations were performed using CFX 4.3, a finite volume based, computational fluid dynamics package. This study represents the first application of the Very Large Eddy Simulation (VLES) approach to the simulation of spray dryers. They have been performed in order to gain a more detailed understanding of the flow patterns and their stability in this design of dryer, which is commonly used in countercurrent drying applications, such as the drying of detergents. Limited validation of the simulations was achieved through comparison against qualitative experimental flow pattern information. It was found that by altering the angle of the inlet air streams into the dryer, the nature of the flow within the dryer could be significantly altered. In the majority of the cases simulated, large transients developed in the flow, the nature of these transients being critically dependent on the inlet conditions. The existence of such transients would be detrimental to actual spray dryer performance, however the flow patterns can be stabilised by introducing a large amount of swirl into the chamber.